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any condition in which the circulatory systemcirculatory system,
group of organs that transport blood and the substances it carries to and from all parts of the body. The circulatory system can be considered as composed of two parts: the systemic circulation, which serves the body as a whole except for the lungs, and the
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 is unable to provide adequate circulation to the body tissues, also called circulatory failure or circulatory collapse. Shock results in the slowing of vital functions and in severe cases, if untreated, in death. It may be caused by inadequate pumping by the heart, by reduction of the blood volume due to dehydration or to loss of blood or plasma, or by reduced blood pressure resulting from dilation of the blood vessels. Inadequate pumping may occur as a result of various kinds of heart disease. Blood loss may result from injuries or from such internal conditions as bleeding ulcers. Burns produce extensive plasma loss from blood vessels into the burned area; crush injuries may result in loss of blood and plasma into the injured tissues. Dilation of blood vessels may be caused by injury to the nervous system, or by pain or emotional stress. Faintingfainting
or syncope
, temporary loss of consciousness caused by an insufficient supply of oxygen to the brain. It can be concurrent with any serious disease or condition, such as heart failure, hypertension (high blood pressure), arrhythmia, hemorrhage, injury to the
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 is a form of shock brought about by a sudden reduction of the blood supply to the brain. Symptoms of shock include weakness, pallor, cold and moist skin, and thirst. The arterial blood pressure is reduced, the pulse is weak and rapid, and the surface veins of the limbs may collapse. Emergency aid for shock victims includes maintaining a clear breathing passage, administering oxygen, controlling bleeding, and keeping the patient warm and in a supine position with legs elevated. Therapy may include blood or plasma transfusion to restore the normal circulation, as well as treatment of the underlying cause of shock. The term shock is also applied to a variety of other conditions such as electric shockelectric shock,
effect of the passage of a current of electricity through the body. Fatality may result from shocks of from 1 to 2 amperes and 500 to 1,000 volts. However, the effect of electric shock on the body depends not only on the strength of the current, but on such
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, allergic shock (see anaphylaxisanaphylaxis
, hypersensitive state that may develop after introduction of a foreign protein or other antigen into the body tissues. When an anaphylactic state exists, a second dose of the same protein (commonly an antibiotic such as penicillin, or certain insect venoms) will
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), and emotional shock. See first aidfirst aid,
immediate and temporary treatment of a victim of sudden illness or injury while awaiting the arrival of medical aid. Proper early measures may be instrumental in saving life and ensuring a better and more rapid recovery.
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a packed conical pile of hay or straw, usually put together where the harvesting takes place. The hay is collected from the fellings when they have a moisture content of 25 to 40 percent and is dried completely in shocks over a period of two to three days. Then the hay shocks are stacked into ricks in the open field, under an awning, or in a barn. About 0.75–2 centners are used to make a rick in areas with a damp climate, and about 2.5–4 centners in dry areas. Hay bucks and harvester-stackers are used to collect the hay into shocks. Gathering straw into a shock is done simultaneously with the combine harvesting of cereals; for this operation the combines are equipped with straw collectors.



a sudden life-threatening condition resulting from severe injury and characterized by progressive impairment of all the physiological systems of the body. The main characteristic of shock is the failure of capillary circulation in the tissues owing to impairment of cardiac output and arterial and venous tonus, capillary dysfunction, and changes in the rheological properties of blood. Shock can be brought on by an injury, burns, surgery (traumatic shock, burn shock, surgical shock), incompatible blood transfusion (hemolytic shock), anaphylaxis (anaphylactic shock), functional cardiac disorders (cardiogenic shock), ischemia of tissues and organs, and excessive loss of blood. The condition was described in detail by the French surgeon H. F. Ledran (1737) and by the Russian physician N. I. Pirogov (1870), who described the symptoms of the erectile phase (brief transient excitement) and torpid phase (subsequent sharp functional inhibition) of shock. The clinical manifestations of shock vary considerably. Progressively increasing extreme weakness and a progressive drop in blood pressure are the most characteristic.

Many aspects of the mechanisms underlying the development of shock still remain unclear. From the neuroreflex viewpoint, the various dysfunctions are due to numerous pain impulses that produce sharp excitation and subsequent inhibition of the nervous system, including the vital centers of the medulla oblongata. From the hemodynamic viewpoint, the decrease in the volume of circulating blood, which leads to peripheral circulatory insufficiency, is the principal factor. From the toxemic viewpoint, shock is caused by the entry into the blood of biologically active substances of tissue origin that interfere with the local and systemic blood flow. It is reasonable to assume that each of these factors plays a part: the primary abrupt activation of the central nervous system by extreme nerve impulses (or toxic substances) increases the amount of catecholamines released into the blood, causing a redistribution of the volume of circulating blood—spasms of the blood vessels of the skin, muscles, kidneys, and abdominal cavity accompanied by the increased flow of blood through arteriovenous anastomoses with maintenance of the circulation in the heart and brain (centralization of the circulation). This period of shock is clinically manifested by pallor and clamminess of the skin, contraction of the pupils, cold perspiration on the face, decreased urine flow, and moderately rapid breathing. The blood pressure is normal or slightly lowered.

“Centralization” of the circulation under conditions of extremely severe and prolonged injury becomes the principal mechanism of circulatory failure and further aggravation of the patient’s condition. The decreased flow of blood to the tissues leads to the accumulation of the products of anaerobic metabolism, biogenic amines, kinins, and other substances. Upon entering the bloodstream, these products, along with other humoral factors, such as increased concentration of some hormones and reduced partial pressure of oxygen, further disrupt the regulatory functions of the nervous system.

The chief factors in the pathogenesis of shock in its late stages are hypoxia, decreased vascular tonus, dysfunction of the tissue microcirculation, and gross derangement of cell metabolism, which results in injury to the cell membranes. The transfer of intravascular fluid to the tissues causes a decrease in the volume of circulating blood. This stage is marked by cyanosis, rapid pulse, lowered blood pressure, and dilatation and slow reaction of the pupils.

The subsequent stage of shock is complicated by congestion in small blood vessels, intravascular agglutination of the erythrocytes, decreased blood flow to the heart, acute cardiac insufficiency, and functional impairment of the vital organs. This stage is clinically manifested by gray cyanosis, thready pulse, abrupt drop in blood pressure, rapid, shallow breathing, dilatation of the pupils, and unconsciousness.

In cases of shock, emergency therapeutic measures are undertaken, chosen according to the cause of the shock, stage of its development, and severity of the patient’s condition. Other measures include the administration of pain relievers, keeping the patient warm, the transfusion of blood and blood substitutes, the administration of oxygen, and the injection of hormones, vitamins, and cardiovascular and other agents.

The term “shock” is also applied to persons in an unusual mental state or persons with severe emotional disturbances (mental, or emotional, shock).


“Problemy reaktivnosti i shoka.” Trudy 1-i Vsesoiuznoi konferentsii patofiziologov. Moscow, 1952.
Petrov, I. R., and G. Sh. Vasadze. Neobratimye izmeneniia pri shoke i krovopotere. Leningrad, 1966.
Weil, M. H., and H. Shubin. Moscow, 1971. Diagnostika i lechenie shoka. (Translated from English.)
Cannon, W. B. Traumatic Shock. New York-London, 1923.
Shires, G. T. Shock. Philadelphia, 1973.



A pulse or transient motion or force lasting thousandths to tenths of a second which is capable of exciting mechanical resonances; for example, a blast produced by explosives.
Clinical manifestations of circulatory insufficiency, including hypotension, weak pulse, tachycardia, pallor, and diminished urinary output.


Pathol a state of bodily collapse or near collapse caused by circulatory failure or sudden lowering of the blood pressure, as from severe bleeding, burns, fright, etc.
References in classic literature ?
There they stood in the big empty field with the quiet corn shocks stand- ing in rows behind them and the red and yellow hills in the distance, and from being just two indif- ferent workmen they had become all alive to each other.
Perkins; "seems like they enjoyed savin' more'n anything in the world, and it's gainin' on Mirandy sence her shock.
He had been so hearty with him, and with them all, that I felt a shock in this unexpected and cold reply.
His answer seemed to shock and thrill me, for it was said as if he did not know that it was me, Mina, to whom he was speaking.
It was a favourable change, and the Tankadere again bounded forward on this mountainous sea, though the waves crossed each other, and imparted shocks and counter-shocks which would have crushed a craft less solidly built.
This it was which had caused the regular beating noise, and the rhythmic shocks that had kept our ruinous refuge quiver- ing.
It follows plainly, in the first place, that the change, of fortune presented must not be the spectacle of a virtuous man brought from prosperity to adversity: for this moves neither pity nor fear; it merely shocks us.
It certainly was a slight armament with which to run the gauntlet through countries swarming with hostile hordes, and a slight bark to navigate these endless rivers, tossing and pitching down rapids, running on snags and bumping on sand-bars; such, however, are the cockle-shells with which these hardy rovers of the wilderness will attempt the wildest streams; and it is surprising what rough shocks and thumps these boats will endure, and what vicissitudes they will live through.
A single drop of the cold fluid seemed to freeze every drop of blood in my body; the fever that had been burning in my veins gave place on the instant to death-like chills, which shook me one after another like so many shocks of electricity, while the perspiration produced by my late violent exertions congealed in icy beads upon my forehead.
As a beginning, D'Artagnan set out in the finest of possible weather, without a cloud in the heavens -- without a cloud on his mind, joyous and strong, calm and decided, great in his resolution, and consequently carrying with him a tenfold dose of that potent fluid which the shocks of mind cause to spring from the nerves, and which procure for the human machine a force and an influence of which future ages will render, according to all probability, a more arithmetical account than we can possibly do at present.
My compasses, of course, were thrown out, my bow was struck twice, and I received two brisk shocks from the lower platform-rail.
No, dearest Georgiana, you came so nearly perfect from the hand of Nature that this slightest possible defect, which we hesitate whether to term a defect or a beauty, shocks me, as being the visible mark of earthly imperfection.